On Wed, 18 Mar 2009, Simon Riggs wrote:
I agree with that, apart from the "granting no more" bit. The most useful behaviour is just to have two modes: * exclusive-lock held - all other x locks welcome, s locks queue * shared-lock held - all other s locks welcome, x locks queue
The problem with making all other locks welcome is that there is a possibility of starvation. Imagine a case where there is a constant stream of shared locks - the exclusive locks may never actually get hold of the lock under the "all other shared locks welcome" strategy. Likewise with the reverse.
Taking a snapshot and queueing all newer locks forces fairness in the locking strategy, and avoids one of the sides getting starved.
Matthew -- I've run DOOM more in the last few days than I have the last few months. I just love debugging ;-) -- Linus Torvalds - Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
